The invention relates to a device for removing solid particles, in particular soot particles, from the exhaust gas of internal-combustion engines, in particular diesel combustion engines. More particularly, the device is of the type including a centrifugal separator or cyclone which separates tangentially supplied exhaust gas into a mostly particle-free pure gas flow and a particle-enriched carrier gas flow. The cyclone has a cylindrical part, a conical part attached thereto, and a collecting part attached to the end of the conical part. A combustion housing in the cyclone includes a supply chamber which receives the carrier gas, a combustion chamber provided with a filter through which the carrier gas flows while exposed to a flame, and an outlet chamber.
In exhaust gas purification devices of the aforesaid kind an agglomerator in which an electrostatic high frequency field is generated is disposed upstream of the centrifugal separator or cyclone in the exhaust gas flow. Electric charging causes the solid particles to coagulate in the high frequency field so as to form larger agglomerates; due to the relative high weight, it is easy to mechanically separate the latter from the exhaust gas flow. The mechanical separation is carried out in a centrifugal separator or cyclone to which the exhaust gas flow containing the agglomerates is supplied at a relatively high tangential flow rate. A rotational flow is generated in the centrifugal separator by means of which the heavy agglomerates are deposited at the external walls; in spirals they travel to the end, e.g. to the bottom, from where they are supplied to a combustion device, together with a small portion of the exhaust gas, as a so-called particle-enriched carrier gas flow. A major portion of the exhaust gas flow centrally emerges from the centrifugal separator as a core flow, mostly free of particles; as a pure gas flow it is supplied to the exhaust system of the combustion engine. Generally, the carrier gas flow heavily loaded with soot or other solid agglomerates amounts approximately 1% of the pure gas flow.
In exhaust gas purification devices of the aforesaid kind disclosed in U.S. Pat. No. 4,649,703 (DE No. 34 24 1961A), the combustion device is provided with a housing which is separate from the centrifugal separator and in which a combustion chamber is inserted. A connecting pipe leads from the collecting piece of the centrifugal separator to the combustion device where it coaxially extends as an immersion tube from the one front side into the housing to end in the combustion chamber. An electrical heater is installed in the combustion chamber. On the side facing away from the immersion tube the combustion chamber itself is open toward the bottom of the housing and there it is provided with a filter disposed downstream of the heater in the exhaust gas flow. The housing has an outlet for the burn-up gases and the filtered carrier gas flow close to the one front side into which the connecting line to the collecting piece ends. An electrical heating maintains the combustion chamber at a temperature between approximately 500.degree. to 600.degree. C. These temperature is sufficient to heat up the soot particles, which are supplied, to the temperature of combustion. Soot particles which were not burnt in the area of the electrical heater are collected in the filter which is disposed downstream. The filter, too, heated up by the gas flow has a temperature sufficiently high to burn soot particles such that the soot particles collected there subsequently completely glow away. The purified carrier gas flow emerging at the filter outlet then flows--annularly enclosing the combustion chamber and immersion tube in a counter current--to the front end and via the outlet into an exhaust gas line. This flow about the combustion chamber and the immersion tube results in a heat recovery such that the electrical heat supply can be reduced. To further improve energy efficiency the housing is well insulated such that the heat loss is maintained at a relatively low level.
In another known exhaust gas purification device disclosed in U.S. Pat. No. 4,672,808 (DE No. 35 26 074 A1), the combustion device is provided with a combustion chamber and a fuel-operated pilot burner. The carrier gas inlet piece which is configured as an immersion tube and connected to the collecting piece of the centrifugal separator ends freely in the interior of the combustion chamber directly before an overflow opening in a chamber wall separating the pilot burner from the actual combustion chamber. A burning fuel-air-mixture coming from the pilot burner is supplied to the combustion chamber via the overflow opening. The flame encloses the end of the immersion tube and burns down in the combustion chamber together with the solid particles supplied via the immersion tube. The combustion products of the burnt-down solid particles and the remaining residual gases, generally referred to as the gaseous burn-up, are, coaxially to the immersion tube, let off via the outlet opening.